Photocatalytic sheet or film and its manufacturing process

ABSTRACT

The invention is directed to a photocatalytic sheet comprising a support, a photocatalytic layer comprising photocatalyst materials and binder, and at least one functional layer wherein said functional layer is in between said support and said photocatalytic layer, wherein said photocatalytic layer and said functional layer are brought on the support using extrusion coating technology or casting technology, as well as to a photocatalytic film sheet comprising: a photocatalytic layer comprising photocatalyst materials and binder, and at least one functional layer, wherein said film is formed by applying casting technology.

FIELD OF INVENTION

[0001] The present invention is directed to the process formanufacturing a photocatalytic sheet by using the extrusion coatingtechnology.

BACKGROUND OF THE INVENTION

[0002] Recently there has been a lot of patents filed where theproduction and use of a photocatalytic coating containing aphotocatalyst material such as titania (TiO₂) is described. The saidphotocatalytic coating find its application in various field oftechnology, such as in the anti-fouling area [U.S. Pat No. 6,013,372]and in antibacterial applications [JP 11047610].

[0003] When a photocatalyst, such as titanium dioxide, is subjected tophotoexcitation by ultraviolet light (UV), water is chemisorbed on thesurface of the titanium ion in the form of hydroxyl groups (OH—) as aresult of the photocatalytic action. As a result, the surface of thematerial coated with TiO₂ becomes very much hydrophilic. Due to saidproperties, a transparent film containing photocatalytic layer can beused as anti fogging material [U.S. Pat. No. 6,013,372].

[0004] Another suggestion on the mechanism of photocatalytic action isthe formation of activated oxygen from water or oxygen in the air whenTiO2 captures UV light. This process is similar to photosynthesis, inwhich chlorophyll captures sunlight to turn water and carbon dioxideinto oxygen and glucose. This activated oxygen has the ability todecompose organic substances and micro-organism which are present nearto the surface of the material that is coated with TiO₂. As a result,the surface which is covered by photocatalytic particles hasantibacterial or disinfecting properties [JP 11047610]. Since theactivated oxygen has the affinity to decompose organic substances, itcan also be applied in a deodorising agent. By coating an aqueousdispersion containing photocatalytic particles and binder on a basepaper, one can produce deodorising paper suitable to be used in aircleaner or for other gas streams [JP 11279446, JP 111171961].

[0005] The most important property of a photocatalyst material is thatupon light radiation with an energy that is higher than the valence bandof the photocatalyst material, an electron and an electron-hole will begenerated by excitation. The excited electron reacts with oxygen andwill decompose the surrounding polymers and other organic materials thathave a lower bonding energy than the valence energy of the photocatalystmaterial by oxidation reaction. As an example, when TiO₂ is irradiatedwith UV light, decomposition of the surrounding polyolefin resin orcellulose will occur. However poly-fluoro-carbon resin will not bedecomposed since the bonding energy of C—F is higher than the valenceband of TiO₂. It is thus of importance to select a suitable material forbeing used as binder for the photocatalytic layer. Examples of suitablebinders for TiO₂ are organic polymers containing fluoro-carbon and/orinorganic materials like silica oxide.

[0006] The conventional method to produce a sheet containingphotocatalysts is by coating an aqueous dispersion containingphotocatalyst particles, inorganic binder, like colloidal silica orsilicone resin, and organic binder, such as a thermoplastic polymerhaving a high deterioration resistance -polytetrafluoroethylene- on afilm or paper. After drying the coating solution, the coated paper isready for cutting and packaging. This method is suggested among othersin JP 11279446, JP 11117196, JP 10128125.

[0007] In JP 11117194, it was proposed to coat the paper with a UVabsorbing layer, followed by coating said layer with a photocatalystcontaining layer that contains expandable microcapsules, and then dryingthe coating by heating. Due to the heat, the microcapsules will expandand create specific desirable surface areas.

[0008] Generally, in order to manufacture photocatalytic film sheets ona support, the layer comprising a polymer with a lower bonding energythan the valence band of the photocatalytic material, should beprotected from a direct contact with the photocatalytic material. Forthis purpose, a protective layer comprising polymer compounds with ahigh bonding energy than that of the photocatalytic layer, are appliedon the support. Thereafter a dispersion solution containingphotocatalyst material, binder and inorganic material are coated on thesurface of said protective layer. The common techniques to apply saidprotective and photocatalyst layers on the support are the coating orspraying methodologies such as dip coating, spin coating, wire barcoating, blade coating, roller-coating, spray coating [JP 07171408].

[0009] The combination of the coating, drying and optional bakingprocesses, which is described in JP 11047610, is known to be slow. As aresult, the production speed becomes low. The more drying and bakingsteps needed, the slower the production speed will be. Anotherdisadvantage of this process is that it costs relatively a lot of energybecause first of all the photocatalytic particles have to be disperseduniformly in the coating solution and secondly evaporating the solventafter coating in the drying or baking step.

[0010] It would be desirable if the photocatalytic film sheet could bemanufactured at a high production speed and without any necessity fordrying or baking processes.

Problem to be Solved by the Invention

[0011] There remains a need for a high speed manufacturing process for aphotocatalyst material that is attached to a support and for aphotocatalyst film sheet.

SUMMARY OF THE INVENTION

[0012] The object of the present invention is to provide a process formanufacturing a photocatalytic sheet at high production speeds.

[0013] It is also an important object of the invention to eliminate thedrying process during manufacturing of said photocatalytic sheet.

[0014] Another object of this invention is to manufacture thephotocatalytic sheet with extrusion coating technology or by castingtechnology and followed by the lamination process. Herein it is includedthat the manufacturing process for a photocatalytic film sheet isapplied by casting technology only.

[0015] A future object of the invention is to concentrate the activephotocatalyst materials in the most upper layer of the photocatalytic(film) sheet, the so called skin layer. It is preferable to have theskin layer as thin as possible.

[0016] Still another object of the invention is to use binders, next tothe photocatalytic material, in the skin layer which are resistant fordeterioration when the photocatalyst is irradiated by UV light.

[0017] The present invention is based on the extrusion coatingtechnology wherein mixtures of fine photocatalyst particles -either asraw material or as a solid dispersion in a polymer resins which is wellknown as master batch- and binder are heated, extruded on the supportsuch as a paper or a polymer film and cooled down by pressing a coolingroll on the extruded support. This technology is not restricted to onelayer extrusion at a time. It is possible to extrude 2, 3 or more layerstogether in a so called co-extrusion method. Another process variation,which is also within the area of this invention, is to apply the castingtechnology which is followed optionally by the lamination process toproduce said photocatalytic sheet.

[0018] According to the present invention, there is provided aphotocatalytic sheet comprising (A) a support, (B) a photocatalyticlayer comprising photocatalyst particles and binder, C) at least onefunctional layer wherein said functional layer is in between saidsupport and said photocatalytic layer, and optionally (D) a polymerresin layer which is introduced between said support and said functionallayer, comprising polymer resins and adhesion promoter additives, andwherein said photocatalytic layer, functional layer and said polymerresin layer are brought onto the support by extrusion coating technologyor a combination of casting and lamination process.

[0019] Also according to the present invention, there is provided aphotocatalytic film comprising (A) a photocatalytic layer comprisingphotocatalyst materials and binder, and (B) at least one functionallayer, wherein said film is produced by casting technology.

DETAILED DESCRIPTION

[0020] The present invention relates, in the broadest sense, of applyingextrusion coating technology, casting technology or the combination ofcasting and lamination process for producing both photocatalytic sheetand photocatalytic film.

[0021] The advantage of this technique is that we do not need todissolve polymer resin, nor the photocatalyst material, binder andinorganic material in water or other solvents prior to extrusion orcasting. We neither need to dry the photocatalytic (film) sheet afterextrusion process since we do not use any solvent. As a result, highproduction speed and an environment friendly manufacturing method forthe photocatalytic (film) sheet is achieved.

[0022] The photocatalytic sheet according to the invention consist of asupport, photocatalytic layer and at least one functional layer betweenthe support and the photocatalytic layer. On the support, which materialis selected from paper, or cellulose, or triacetylcellulose (TAC) orpolyethyleneteraphtalate (PET), polyethylenenaphtalate (PEN), orpolyamide or polypropylene other polymeric films, resides at least onefunctional layer. The said functional layer may have several differentfunctions, such as (1) to provide protection to the layer underneath thefunctional layer from the photocatalyst which is present in thephotocatalytic layer, (2) to provide a good adhesion between the layerunderneath and the layer above this functional layer and (3) to provideadditional features to the sheet such as addition of some colour, flameretarding properties. The said functional layer comprising of binder,polymer resin, filler, extenders, pigment, and optionally dye andadhesion promoter additives. On the top of the functional layer residesthe photocatalytic layer comprising photocatalyst materials and binders.

[0023] In this invention we can optionally introduce one or more polymerresin layer between said support and said functional layers. The saidpolymer layer has two primary functions i.e. (1) to provide a goodadhesion between the support and the functional layer and (2) to createa good condition for the co-extrusion process. By having the saidpolymer resin layer, the co-extrusion process becomes more easy tocontrol and makes the production of photocatalytic sheet moremanufacturable. In some cases it may be necessary to apply two polymerresin layers on the support to enhance the stability of manufacturingprocess and improve adhesion properties of the sheet.

[0024] The extrusion coating is preferably done by the co-extrusionmethods, wherein the functional layer, optionally polymer resin layerand the photocatalytic layer are extruded at the same time on thesupport. The layer formation is arranged as such that the functionallayer is positioned in between the support and the photocatalytic layer.In case a polymer resin layer is included, this layer is positioned inbetween the support and said functional layer.

[0025] The structures of the photocatalytic sheet of the invention arethus as follows: Photocatalytic Photocatalytic Functional layer AndFunctional layer Support Polymer resin Support

[0026] In this invention we also apply casting technology in order toproduce a photocatalytic film consisting of a photocatalytic layer andat least one functional layer. As in the case of the extrusion coating,we optionally may have one or more polymer resin layer(s) too. Herein,the photocatalytic layer, the functional layer and optionally thepolymer resin layer are melted and fed onto the cooling roll. Thephotocatalytic film has the following structure: Photocatalytic layerPhotocatalytic And Functional layer Functional layer Polymer resin

[0027] It is still within the spirit of this invention to produce saidphotocatalytic sheet by, first of all, producing the photocatalytic filmand then laminated said film on a support.

[0028] Both the co-extrusion as well as the casting techniques areespecially suitable for manufacturing thin photocatalytic layer at ahigh production speed. The thickness of the photocatalytic layer isimportant for the effectiveness of the photocatalytic (film) sheet sinceonly photocatalyst materials present on the surface will be effectivelyused by UV radiation. The thickness of the photocatalytic layer isbetween 0.1 to 5.0 μm, preferably between 0.1 μm to 2.0 μm and morepreferably between 0.3 to 1.0 μm. The total thickness of thephotocatalytic sheet, excluding the support, is at least 10 μm

[0029] The extrusion coating can also be done by multiple extrusion, orcombination of co-extrusion and single or multiple extrusion. In thiscase one or more polymer resin layer(s) and the photocatalytic layer canbe extruded subsequently on the support. After each extrusion process,the surface of the polymer resin layer can be treated with coronatreatment, ozone treatment, plasma treatment, flame treatment or coatedwith an adhesion promoter additives, which purpose is to improve thesurface properties of the protective layer.

[0030] By combining single or multiple extrusion and co-extrusion, anenormous variations of the thickness and the amount of layers ofphotocatalytic layer and protective layer(s) can be achieved.

[0031] The advantage of the co-extrusion above multiple extrusioncoating is that a thin and high concentrated photocatalytic layer can beextruded, especially at photocatalyst concentration higher than 10 wt %.Another advantage is that co-extrusion has wider process operationwindow compared to multiple extrusion. It is relatively more easy forco-extrusion process to control the adhesion between the layers.

[0032] In this invention, the suitable photocatalyst material isselected from the group consisting of SrTiO₃, TiO₂, ZnO, SnO₂, WO₃,Fe₂O₃ and Bi₂O₃. The preferred photocatalyst material is the anataseform of TiO₂.

[0033] The photocatalytic layer comprising of 10 wt % to 90 wt % ofphotocatalyst material and 90 wt % to 10 wt % binder having higherbonding energy than the photocatalyst. The effectiveness ofphotocatalytic material at concentration lower than 10 wt % is so lowthat it is regarded as not desired, whereas at concentration higher than90 wt %, the extrusion and casting processes are expected to beunstable.

[0034] Preferably, the photocatalytic layer contains 20 wt % to 80 wt %of photocatalyst materials and 80 wt % to 20 wt % binder.

[0035] The organic binder for the photocatalytic layer is selected fromany combination or mixture of monomers that is selected from the groupof tetrafluoroethylene or vinylenedifluoro or hexafluoropropylene orperfluorovinylether or any other monomer containing fluor-carbonbonding.

[0036] The functional layer which provides, among others, protection tothe polymer resin layer having a bonding energy lower than the valenceband of the photocatalyst material, contains next to the said binder,also polymer resin and at least pigments and fillers or extenders.Depending on the additional function of the layer, we may optionally addother additives such as dye, adhesion promoter, matting agents, antioxidant and processing aids. The purpose of the extender or fillermaterials is to increase the desired volume of the functional layer witha cheaper material than the binder. The amount of fillers in saidfunctional layer lies between 5 wt % to 60 wt %. The fillers can beselected from silicious particles, calcium-carbonate, pigment gradeTiO₂, hydrated aluminium oxide and clay. The non-limiting examples ofsilicious particles are: silica, mica, montmorillonite, kaolinite,zeolites, aluminium polysilica, etceteras. The pigments can be selectedfrom the inorganic pigments, the organic pigments or combination of it.Suitable inorganic pigments are the white pigments such as pigment gradeTiO₂, zinc oxide and zinc-sulphate, the iron oxide pigments, theultramarine pigments, or the blue iron pigments. The suitable classes oforganic pigments include azo pigments, metal-complex pigments such ascopper phthalocyanine and higher polycyclic compounds such asanthraquinone, isoindolinone and perylene.

[0037] The suitable material for the polymer resins used in the polymerresin layer can be selected from thermoplastic polymer classes-thatinclude polyolefin, polyesters, polyamides, polycarbonates, cellulosicesters, polystyrene, polyvinyl resins, polysulfonamides, polyethers,polyimides, fluoro polymers, vinyl polymers and vinylidene polymers,polyurethanes, polyphenylenesulfides, polytetrafluoroethylene,polyacetals, polysulfonates, polyester ionomers, polyolefin ionomers,polymetacrylate, polymethylacrylate, polyethylacrylate.

[0038] Suitable polyolefins include polyethylene, polypropylene,polymethylpentene, polycyclohexylethylene, polyoctene, polynonene.Polyolefin copolymers, including copolymers of propylene and ethyleneand mixture thereof such as hexene, butene and octene, cyclo-olefins andstyrene are also useful. Other copolymers contains ethylenecarbonmonoxide, styrene-acrylonitril, ethylene vinylacetate, acrylicacid, methacrylic acid and styrene-acrylonitril, can also be selected.

[0039] Vinyl and vinylidene polymers are selected frompolyvinylchloride, polyvinylidenechloride, polyvinylalcohol,polyvinylacetal, polyvinylbutyral, and copolymers like ethylenevinylalcohol.

[0040] Suitable fluoro polymers are polyvinyl fluoride, polyvinylidenefluoride, polytetrafluoroethylene, copolymer of ethylenetetrafluoroehtylene, polychlorotrifluoroethylene and its copolymers withethylene or tetrafluoroethylene-hexafluoropropylene. The composition ofthe polymers used depends very much on the functional layer. Selectionof polymers will be mainly based on enhancing the adhesive propertiesbetween the support and said functional layer, and achieving optimumcondition for co-extrusion process.

[0041] The invention is now elucidated on the basis of the attachedFIGS. 1 and 2. In FIG. 1, a co-extrusion line for laminating a supportis shown. The support is fed via a number of rollers. Between thefeeding roller and the cooling roll both the support and all layers ofpolymer melt including the photocatalytic containing layer are fed. Thepolymers are pressed by the niproll to the support which is cooled downby the cooling roll, and thereafter the laminated support is transportedfurther.

[0042] In FIG. 2, a casting line for manufacturing the film sheet isshown. The melt polymer layers, including the photocatalyst layer, arefed onto the cooling roll. In order to lead the melted polymer onto thecooling roll, we may apply air-knife or electrostatic pinningmethodology. The film is thereafter transported further and it is readyfor the lamination process.

[0043] The die used for feeding the melted polymers layer can be amulti-manifold die, or feed-block system or the combination of multimanifold and feed-block.

[0044] The present invention is further described with reference to thefollowing examples, but it should be construed that the invention is inno way limited to those examples.

EXAMPLES Example 1.

[0045] The following sheet was made by a co-extrusion process.

[0046] Hopper 1 was filled with a fluoropolymer masterbatch containing15 wt % TiO₂. The TiO₂ was purchased from Ishihara, type St-41, and thefluoropolymer from Dyneon, type THV 220G. Hopper 1 was connected to a2.5 inch single screw extruder 1.

[0047] Hopper 2 was filled with LDPE which had a Melt Flow Index of 2(DSM grade) and was connected to a 2.5 inch single screw extruder 2.

[0048] These 2 screw extruders were combined in a two layerfeedblock/coathanger die. The extrusion temperature was 210° C. Thearrangement of the layers was done as such that the polymer from hopper2 resided on the surface of base paper and the content of hopper 1formed the most upper layer. The support which was a 166 g/m2 basepaper, was fed via a number of rollers at a speed of 30 m/min, and wascorona treated before entering the nip. In the nip, the melt polymer wasozone treated and was pressed by the cooling roll onto the base paper.Thereafter, the laminated support was transported further for evaluationand for sample taking.

[0049] The thickness of each layers obtained from this experiment was3μm for the photocatalytic layer containing TiO₂ and 20μm for the PElayer.

[0050] Measuring Method for the Photocatalytic Activity.

[0051] A square box, W×L×H=8.8 cm×19.0 cm×9.4 cm, was filled with 100 mlwater solution of cyan anti-halation dye, which containing a pyrazolonederivative (Sankyo Chemicals-Japan). The concentration of the cyan dyesolution in the box was 100 mg/L.

[0052] A photocatalytic sample with a surface area of 115 cm², was fixedon the bottom of the box. The box was then radiated with a 6 Watts UVlamp 9815 series from Cole Parmen. The radiated surface area of theliquid was 133 cm². The distance between the UV lamp and the surface ofthe liquid was 10.0 cm and that between the UV lamp and the surface ofthe photocatalytic sample was 12.5 cm. Under this condition, the cyandye was decomposed by the photocatalytic film.

[0053] The concentration of the cyan dye was measured regularly by usingUV/VIS spectro-photometer (Hewlett Packard 8453) at a wavelength of 645nm. And the results are shown in table 1.

Example 2.

[0054] Hopper 1 was filled with a fluoropolymer masterbatch containing30 wt % photocatalyst grade TiO₂. The TiO₂ was purchased from Ishihara,type St-41, and the fluoropolymer from Dyneon, type THV 220G. Hopper 1was connected to a 2.5 inch single screw extruder 1.

[0055] In hopper 2, a 60 wt % master batch of pigment grade TiO₂ inLDPE, was mixed together with fluoropolymer, THV and low densityPolyethylene (LDPE) MFI-8 purchased from DSM in such away that the finalconcentration of pigment grade TiO₂ in the hopper was 30 wt %, theamount of fluoropolymer was 30 wt % and the concentration of LDPE was 40wt %. Hopper 2 was connected to a 2.5 inch single screw extruder 2.

[0056] In hopper 3 LDPE MFI-8 from DSM was stored and this hopper wasconnected to a 4.5 inch single screw extruder 3.

[0057] These 3 screw extruders are combined in a three layerfeedblock/coathanger die. The melt temperature is 210° C. Thearrangement of the layers was done as such that the polymer from hopper3 resided on the surface of base paper, the content of hopper 2 residedon the surface of polymer from hopper 3 and the content of hopper 1formed the most upper layer. The support which was a 166 g/m2 basepaper, was fed via a number of rollers at a speed of 200 m/min. and wascorona treated before entering the nip. In the nip, the melt polymer wasozone treated and was pressed by the cooling roll onto the base paper.Thereafter, the laminated support is transported further for evaluation,and packaging.

[0058] The thickness of each layers obtained from this experiments wasas follow:

[0059] layer 1, containing 30 wt % of photocatalyst grade TiO₂ and 70 wt% fluoropolymer: 0, 5 μm

[0060] layer 2, containing 30 wt % of pigment grade TiO2, 30 wt %fluoropolymer and 40 wt % LDPE MFI-8: 3 μm

[0061] layer 3, containing LDPE MFI-8 only: 10 μm

[0062] The photocatalytic activity of the sheet was measured accordingto the method mentioned in example 1 and the results are listed intable 1. TABLE 1 Concentration of cyan dye Time in the box [%] [minutes]Example 1 Example 2  0 100  100   30 86 96  60 69 85  90 52 76 120 42 68150 30 60 180 23 55 210 15 49

1. A photocatalytic sheet comprising a support, a photocatalytic layercomprising photocatalyst materials and binder, and at least onefunctional layer wherein said functional layer is in between saidsupport and said photocatalytic layer, wherein said photocatalytic layerand said functional layer are brought on the support using extrusioncoating technology or casting technology.
 2. The sheet of claim 1,further comprising one or more polymer resin layer(s) wherein saidpolymer resin layer or layers reside between the support and the saidfunctional layer.
 3. A photocatalytic film sheet comprising: aphotocatalytic layer comprising photocatalyst materials and binder, andat least one functional layer, wherein said film is formed by applyingcasting technology.
 4. The film sheet of claim 3, further comprising oneor more polymer resin layer(s) wherein said functional layer residesbetween the said polymer resin layer and the said photocatalytic layer.5. The sheet of claim 1 or 2, wherein co-extrusion technology is appliedto extrude all said layers on the support.
 6. The sheet of claim 1, 2 or5, wherein said support is a paper or polymeric films such astriacetylcellulose or polyethyleneteraphtalate or polyethylenenaphtalateor polyamide or polypropylene.
 7. The sheet of claims 1-6, wherein thetotal thickness of the photocatalytic sheet is at least 10 μm.
 8. Thesheet and film sheet of claims 1-7, wherein the functional layercomprises at least binders, polymer resins, extenders or fillers andpigments.
 9. The sheet and film sheet of claims 1-8, wherein saidphotocatalyst material is an oxide selected from the group consisting ofSrTiO₃, TiO₂, ZnO, SnO₂, WO₃, Fe₂O₃ and Bi₂O₃.
 10. The sheet and filmsheet of claims 1-9, wherein said photocatalyst material comprises theanatase form of TiO₂.
 11. The sheet and film sheet of claims 1-10,wherein said photocatalytic layer contains a photocatalyst in an amountbetween 10 and 90 wt %, preferably between 20 and 80 wt %.
 12. The sheetand film sheet of claims 1-11, wherein said photocatalytic layercontains said binder in the range between 10 and 90 wt %, preferablybetween 20 and 80 wt %.
 13. The sheet and film sheet of claims 1-12,wherein said photocatalytic layer has a thickness of 0.1 μm-5 μm. 14.The sheet and film sheet of claim 13 wherein the thickness of saidphotocatalytic layer lies between 0.1 μm and 2.0 μm.
 15. The sheet andfilm sheet of claim 13 and 14 wherein the thickness of saidphotocatalytic layer lies between 0.3 μm and 1.0 μm.
 16. The sheet andfilm sheet of claims 1-15 wherein said binder is a polymer based on anycombination of monomers selected from the group of tetrafluoroethylene,vinylenedifluoro-, hexafluoropropylene, perfluorovinylether and mixturesthereof.
 17. The sheet and film sheet of claims 8-16 wherein saidfillers or extenders are selected from the group of silicious particles,calcium-carbonate, TiO₂, hydrated aluminium oxide and mixtures thereof.18. The sheet and film sheet of claims 8-17 wherein said pigments areselected from the group of TiO₂, zinc-oxide, zinc-sulphate, the ironoxide pigments, the ultramarine pigments, the blue iron pigments, theazo pigments, copper phthalocyanine, isoindolinone, perylene andmixtures thereof.
 19. The sheet of claims 2-18 wherein said polymerresin is selected from thermoplastic polymers.
 20. The sheet of claim 19wherein said polymer resin is selected from the thermoplastic polymerclasses that include polyolefin, polypropylene and polymethylpentene.21. Process for the manufacture of a photocatalytic sheet according toany one of the claims 1,2 or 5-20, said photocatalytic sheet comprisinga support, a photocatalytic layer comprising photocatalyst materials andbinder, and at least one functional layer wherein said functional layeris in between said support and said photocatalytic layer, wherein saidphotocatalytic layer and said functional layer are brought on thesupport using extrusion coating technology or casting technology. 22.Process for the manufacture of a photocatalytic film according to anyone of the claims 3-20, said photocatalytic film comprising aphotocatalytic layer comprising photocatalyst materials and binder, andat least one functional layer, wherein said film is formed by applyingcasting technology.